1. Technical Field
The present invention relates to a radiological image conversion panel, a method of manufacturing a radiological image conversion panel, and a radiological image detection apparatus equipped with the radiological image conversion panel.
2. Description of Related Art
Recently, a radiological image detection apparatus that utilizes a flat panel detector (FPD) detecting a radiological image to create digital image data has been commercialized, and is widely distributed because the image is instantly checked as compared with an imaging plate according to a related art. Various types of radiological image detectors are available and one of them is known as an indirect conversion type radiation image detector.
The indirect conversion type radiological image detection apparatus includes a scintillator (phosphor) made of a fluorescent material such as cesium iodide (CsI) that produces fluorescence by the radiation exposure and a sensor panel in which a plurality of thin film type photoelectric conversion elements are two-dimensionally arranged on a substrate. The radiation that penetrates a subject is converted into light by the scintillator of the radiological image conversion panel and the fluorescence of the scintillator is converted into an electrical signal by the photoelectric conversion elements of the sensor panel, thereby generating image data.
A technology that forms the scintillator with a group of columnar crystals that is formed by growing a crystal of a fluorescent material such as CsI by a vapor deposition method in a columnar is also known (see, for example, WO 2008/029610 A, WO 2010/029779 A and JP-A-2011-017683). The columnar crystals formed by the vapor deposition method does not contain impurities such as a bonding agent, and has a light guide effect that directs the fluorescence generated therein in a growth direction of the crystal to suppress the diffusion of the fluorescence. Therefore, not only the sensitivity of the radiological image detection apparatus, but also a sharpness of the image is improved.
In a radiological image conversion panel disclosed in WO 2008/029610 A, in order to increase the light gathering efficiency of the fluorescence, tips of individual columnar crystals are formed to be a convexed shape having a tip angle at about 40 degrees to 80 degrees.
Herein, a crystal of CsI has a deliquescent property and thus causes the columnar crystal structure collapses by absorbing moisture to reduce the light guide effect. Therefore, the scintillator formed by the columnar crystal of CsI is typically covered by a protection film made of polyparaxylylene in order to provide a moistureproofing property. The polyparaxylylene protection film is generally formed by the vapor deposition method.
The polyparaxylylene protection film formed by the vapor deposition method may be inserted into a deep portion between the columnar crystals. The light guide effect of the columnar crystal is generated by the total reflection generated by a difference in refractive indexes between the columnar crystal and the surrounding medium. Though the surrounding medium is air, if the protection film is inserted into the deep portion between the columnar crystals to cover around the columnar crystal, the refractive index of the polyparaxylylene that forms the protection film is bigger than that of air. As a result, the difference in the refractive indexes between the columnar crystal and the surrounding medium becomes small, so that the total reflection is suppressed to reduce the light guide effect as described above.
Therefore, in a radiological image conversion panel disclosed in WO 2010/029779 A, the protection film is formed by applying a gel type curable resin so that the protection film fills only between the tips of the columnar crystal group, but does not reach the deep portion between the columnar crystals.